This study is designed to provide information on Alpha-N-acetyl-Beta-endrophin and Alpha-N-acetyl-C'-fragment (i.e. acetylated Beta-endorphin derivatives in rat brain membranes and in cultured neuroblastoma cells (N4TGl) and neuroblastoma-glioma hybrid cells (NG-108). The experimental approach is to chemically prepare acetylated peptides from the parent compounds and tritiate these to high specific radioactivity using tritiated sodium borohydride in reductive methylation. Binding studies will be performed in vitro where putative receptor affinity and levels can be estimated. If receptors are found for the acetylated peptides, we will ascertain whether these are opiate receptors or not. This study should provide information on possible physiological roles for Alpha-N-acetylated Beta-endorphin and C' - fragment. If no receptors can be identified, this would suggest that acetylation in vivo may be regulated inactivation process.